This is a really bad idea
Tis is one of those ideas where the longer you think about it, the worse it looks.
Any kind of hardware device intended to prevent speeding is a bad idea. There are situations where the *only* safe thing to do is temporarily to break the speed limit -- for instance, what if something is coming at you from behind and the opposite lane is unavailable? Are we just supposed to crash like good little martyrs, safe in the knowledge that someone else was at fault?
And the ability remotely to stop a vehicle is also worrying. If (a tiny subset of) the Good Guys can use it, then we have to assume that the Bad Guys can use it too.
What will happen -- I can predict this quite confidently -- is that someone absolutely without malicious intention will discover how to turn off their own car. It may not have happened yet; but then again, the technology simply isn't common enough or cheap enough. More cars which can be disabled remotely means more opportunities to try remotely to disable a car.
At first, of course, it'll only be used as a humorous party trick. Then, the same discovery will be made independently somewhere else (cf. the invention of the incandescent light bulb). But a trick is no good without an audience, and it will be shown off. At some point, the technique will reach the criminal fraternity. Not the "nice" criminal fraternity who just do vaguely illegal things like grow a bit of weed, chase off a bunch of hunters, blow stuff up in out-of-the-way places or not pay for some of their toys; but the "nasty" criminals who do the really illegal stuff like people-smuggling, gun-running and terrorism and aren't afraid to maim and kill to get what they want.
Some technically-bright but socially-dim kid will get out of their depth with a criminal gang and end up with an ultimatum: build a remote car-stopper for them, or else. The gadget will be cloned in third-world sweatshops {if not first-world sweatshops} before the day is out, and used for crime. The only solution in the end will be to scrap the remote disabling ability altogether.